MODIS LAI Product in West Java Province Weather Condition in the Study Area

Figure 4 The yearly rainfall from year 2004 year until 2008. The temperature was corrected using elevation data which were derived from DEM data. According to Braak formula 1929 in Ritung et.al. 2007, the temperature in Indonesia will decrease by 6.1 C regularly every increasing 1000 m above sea level. Figure 5 shows the yearly average of temperature for 5 years in West Java province. It varied from 10 C until 26 C. The minimum temperature associated with high elevation which it located on top of mountain while the maximum temperature founded near of low-land area. Figure 5 Yearly average temperature from year 2004 until year 2004. Daily relative humidity, solar radiation, and wind speed were directly used as an input of the model. The statistical downscaling was used to change the spatial resolution of those data into 1 x 1 km. Even though coarse resolution influenced by the accuracy, it was suitable for regional crop yields forecasting over regions which have sparse weather station de Wit et al., 2010. Table 3 gives the summary of weather variables such as temperature, RH, solar radiation, wind speed and rainfall in the study area. Table 3 Average yearly temperature, RH, solar radiation, wind, and rainfall Year Temperature C RH Solar Radiation MJm 2 Wind ms Rainfall mm 2004 23.8 84.8 13.0 2.9 2606 2005 24.1 84.8 12.2 2.8 2680 2006 23.8 84.8 13.1 3.2 2143 2007 23.8 85.6 12.6 3.1 2864 2008 23.7 85.9 12.7 3.3 2374

4.3. Yield Simulations

The simulations were run in 16 regencies in west Java during 2004 – 2008 with the assumption the paddy field area was constant. In each grid, the model simulates the rice yield every day along the life cycle of rice crop. The final yield in each grid will be aggregated to determine rice yield in regency level or the next level. Figure 6 shows comparison between model result and BPS report in West Java province. Reference data BPS shown the yield has increased 0.5 tha during 5 years. But the rate increased has slowed in period 2004 until 2005 and constant from year 2005 until 2006 year. The yield from the model fluctuated a lot and tended decreased over the period of 5 years. The differences between model and BPS in year 2004 is 0.2 tha, rises 0.5 tha in year 2005, becomes more than five times from 2004 with 0.11 tha in year 2006 and slow down with 0.6 tha in 2007. The close difference between model and BPS data found in 2007 with 0.1 tha. Figure 6 Comparison of estimated yield and BPS report in West Java province. Figure 7 shows an example of yield images in 2006 and 2008, was generated by the model. It shows a large visual contrast especially in the north region of West Java province between year 2006 and year 2008. In year 2006, the yields from Bekasi, Karawang, Subang, and Indramayu regency were varied starting from below 3 tha until 4 tha while in year 2008 it ranged from 3 tha until 5 tha. Figure 7 Rice yield in year 2006 until year 2008 in West Java province.